Alternating current-direct current interchanging system and control therefor



July 20, 1937. c. F. STRONG 2,087,659

ALTERNATING CURRENT-DIRECT CURRENT INTERCHANGING THEREFOR SYSTEM ANDCONTROL Filed March 51, 1933 Patented July 20, 1937 UNITED STATES PATENTOFFICE ALTERNATING CURRENT-DIRECT CURRENT INTERCHANGING SYSTEM ANDCONTROL THEREFOR Claims.

This invention relates to automatic prime mover operated generatingequipment and more particularly to an improved alternating current anddirect current energy interchange appara- 5 tus and control meanstherefor.

It is one object of my invention to provide an improved automatic primemover operated a1- ternating current generating system employinginternal combustion engines preferably of the Diesel type and to have ahighly satisfactory degree of voltage regulation. A further object is toprovide an improved energy interchange system and controls whereby asource of auxiliary direct current, such for example as a storagebattery, may be efiectively employed to insure proper voltage on the A.C. side of the system. Another and more specific object is to provide animproved arrangement of fields on a D. C. dynamo electric machine incombination with a field of an A. C. dynamo electric machine whereby thecurrent for these two sets of fields may be so controlled andcoordinated that substantially constant voltage will be maintained onthe A. C. system together with battery charging.

Other objects and advantages will be more apparent -to those skilled inthe art from the following description of the accompanying drawing whichis a wiring diagram of my improved system and the controls therefor.

In the accompanying drawing which merely illustrates one specificembodiment the inventicn might take among other possible forms, there isshown a storage battery I, a direct ourrent dynamo electric machine 27asynchronous type alternating current dynamo electric machine 3, and anexciter .4 for machine 3. The rotating members of machines 2, 3, and 4are either mounted on a common shaft or so connected as to rotate inunison.

A synchronous type A. C. generator 5 is driven by an engine 6 or someother source of power so governed as to maintain an approximatelyconstant speed under varying loads. Wires 1,

5 8, and 9 represent a three phase alternating current circuitconnecting with a variable load l0.

Direct current machine 2 is connected to battery I through leads H, l2,and 13, starting box I4 and series field l5 to battery I. A major 50shunt field for machine 2 is generally indicated at IS. A field I8 iswound so as to assist field l6 for excitation purposes while a field I1is wound so as to oppose field l6. Fields I! and I8 are preferably ofapproximately the same 55 ampere turns so that if both fields aresimultaneously supplied with the same number of amperes, their opposedpolarity will neutralize the effect of each other.

A regulator generally indicated at H! controls field Hi. This regulatorcomprises a solenoid 2B 5 connected to A. 0. lines 8 and 9 while acarbon pile resistance M is in series with shunt field l6 as through awire 22, a hand operated field rheostat 23 and wires 24 and 25 tobattery 11, the other side of field it; being connected to the plus 10side of the battery as through wires 26, starting box l4 and wire l3.

Field W of direct current machine 2 is connected in series with a fieldexcitation coil 25 of alternating current machine 3 and the amount 5 ofcurrent flowing through these fields is controlled by a regulator 21whose solenoid 28 is connected to A. C. lines 8 and 9 of the three phasecircuit ll, 8. and 9. The field 26 is shown as of the rotating typeconnected to fields H and wire 37! through slip rings although ifdesired the field 26 may be stationary and a revolving armatureemployed. A carbon pile resist ance 29 is in series with fields I1 and26 which are supplied with current by exciter 4. The field ill ofmachine 2 is controlled by a regulator 30 whose solenoid 3! is connectedacross A. C. lines 8 and 9 while a carbon pile 32 of the regulator is inseries with field I8. Field l8 receives its supply of current fromexciter 4. It will be 30 noted that each of the regulators has a pivotedlever 19, 27', and 30 connected to their respective solenoid cores andadapted to variably press on the carbon piles in. accordance withadjustments of springs 2|, 34, and 32.

In operation, if machines 2, 3, and 4 are not operating and machine 5 isalso not operating, machines 2, 3, and 4 may be started from the batteryby operation of starting box M. Machine 5 may then be started by currentfrom lines I, 8, and 9 or by starting engine in accord-- ance with anyaccepted Diesel practice. A. C. machine 3 may then be synchronized withA. 0. machine 5 by adjustment of field rheostat 23 and operation of anyusual switching mechanism 33. Rapid changes in load I0 may be of suchproportion that generator 5 may be unable to respond to them rapidlyenough and also there may be undue voltage variation on lines I, 8, and9. Furthermore, the load may, for short periods, go beyond the abilityof generator 5 and engine 6 to supply the necessary energy. The purposeof machines 2, 3, and 4 and the} control regulators i9, 21, and 30 is tosecure the necessary accurate voltage regulation and to interchangeenergy between A. C. lines I, 8, and 9 and battery I whenever such maybe necessary.

If machine 5'is being driven by engine 6 so as to supply current at thedesired voltage to lines "I, 8, and 9, then machines 2, 3, and 4 andtheir regulators I9, 27, and 30 and field rheostat 23 are so set thatmachine 2 is neither charging battery I nor motorizing to cause machine3 to deliver power to lines 1, 8, and 9. Machine 3 therefore simplyoperates in synchronism with machine 5 so as to float on the line. Anyaddition of a heavy load at IU of sufiicient magnitude to cause a fallin voltage across lines 8 and 9 will cause regulator 21 to act onaccount of its solenoid 28 being opposed by an adjustable spring 34.Hence with a drop in voltage, there is a loss of pull by solenoid 28thus allowing spring 34 to exert pressure on carbon pile 29 and therebyincrease current fiowing in fields I l and 26. Increase of current incoil 26 tends to raise voltage of machine 3 and at the same time fieldI'I acts differentially against shunt coil I6 to cause a loss of fieldon machine 2 thereby causing it to motor and draw current from batteryI. Series coil I5 is so proportioned as to oppose coil I6 only to suchan extent that under these load conditions the internal resistance dropof battery I and armature of machine 2 will be compensated for. Thus thespeed of machine 2 and its torque will be maintained to drive machine 3as a generator.

If the duration of demand for current from machine 3 is short, then upontermination of such demand, regulator 21 returns to its, normal settingso that generator 5 again carries all the load. If however the increaseddemand should continue, then machine 3 must deliver energy to the A. C.line to meet this increased demand, in which case battery I will developa considerable polarization drop of voltage with consequent loss oftorque from machine 2 for driving machine 3. Under such conditionsregulator I9 is set to act at a very slightly lower voltage than thesetting for regulator 21 and regulator I9 causes carbon pile resistance2| to so act as to increase resistance in circuit of field I6 andthereby cause machine 2 to take more current to compensate for loss ofvoltage in battery I and thus continue to act as a motor for drivingmachine 3 as a generator.

Under certain circumstances, it is a possibility that by proper designof field I6 the regulator I9 may be omitted and resistance 23 connectedto wire 25 as by wire 24', and then any drop in volage in the batterydue to polarization will cause a proper proportionate loss in field I6,thus automatically increasing the motorizing effect to allow for thefalling voltage of the battery.

In the event that the voltage on the line 1, 8, and 9 has a tendency torise above the normal value due to any usual conditions, such as reducedload or otherwise, regulator I9 has its carbon pile fully compressed torestore field I6 to normal strength while resistance of pile 29 isincreased due to regulator 21 having its arm 35 brought to rest againsta stop 36 thereby reducing or cutting out the diiferential action offield I1. The increased line voltage also causes solenoid 3| to increasepressure on carbon pile 32 thereby causing energization of field I8 tobe increased and accordingly increase the field strength on machine 2with the result that machine 2 loses its motoring effect and now servesas a generator, the

A. C. machine 3 drawing current from the line and inherently serving asa motor under such circumstances to drive machine 2 as a generatorthereby to charge the battery.

To those versed in the action of synchronous alternating currentgenerating and motor characteristics, it is evident that machine 3remains in synchronism with machine 5, the changing of machine 3 from amotor to a generator or vice versa being caused merely by shifting itspole position in relation to the phase of the current on line 1, 8, and9. This shifting is effected merely by placing a positive or negativetorque on D. C. machne 2 as by varying its field strength to make itserve either as a motor or generator.

It is preferable that regulator 21 is adjusted so that for full currentfiow through its carbon pile, the field excitation of machine 3 isincreased only sufliciently for effecting full load output atsynchronous speed. Also the tendency of the field for machine 3 is,preferably, to be slightly overexcited, thus tending to cause themachine to act as a synchronous condenser, but it should not be too highso as to disturb line voltage conditions.

From the foregoing disclosure it is seen that I have provided arelatively simple and effective arrangement for insuring proper voltageregulation in an alternating current system together with an amplesource of reserve current in a system carrying temporary excessiveloads. While I have shown one specific form that the invention mighttake, it will of course be understood that in various practicalembodiments of the invention there may be changes in details andarrangement of parts without departing from the spirit.

of the invention claims.

I claim:

1. An alternating current generating system comprising, in combination,an A. C. dynamo electric machine normally connected to the line load, D.C. and A. C. dynamo electric'machines operatively connected to eachother, said latter A. C. machine also being connected to the load line,and voltage responsive means for controlling the field strength of eachof said operatively connected machines independently of line current.

2. A generating system comprising, in combination, an A. C. dynamoelectric machine adapted to normally supply line load, another A. C.dynamo electric machine connected to the line and having a suitablefield, a D. C. dynamo electric machine operatively connected to saidlatter A. C. machine, opposed fields for said D. C. machine, and meansfor controlling all of said fields automatically in accordance withvariations in line voltage thereby to maintain substantially constantline voltage independently of line current.

3. A generating system comprising, in combination, an A. C. dynamoelectric machine adapted to supply line load, another A. C. dynamoelectric machine connected to the line, a D. C. dynamo electric machinefor driving said latter A. C. machine and having a shunt field and twofields of opposed polarity, and means for variably adjusting said latterfields automatically in accordance with variations in line voltage aboveor below normal thereby to variably control said A. C. machine that isconnected to the D. 0. machine and thus control the line voltage tomaintain it substantially constant.

A generating system comprising, in combination, a prime mover operatedC. dynamo electric machine adapted normally to supply line load, a C.A.C. dynamo electric machine unit with the A. machine thereotco ected tothe line, fields tor each. of the mile of. said unit,

as set forth in the appended means for variably controlling each of saidfields thereby to cause the A. C. machine of said unit to either lead orlag automatically in accordance with variations in line voltage above orbelow normal thus to maintain substantially constant line voltageindependently of line current, and a storage battery for supplyingcurrent to the D. C. machine of said unit whereby in line voltages abovenormal the A. C. machine of said unit will tend to drive the D. C.machine thereof thereby to in charge said battery.

CHESTER F. STRONG.

